Particle formation

Abstract

Method for preparing a target substance in particulate form, by introducing into a particle formation vessel, through separate first and second fluid inlets respectively, (a) a solution or suspension of the target substance in a fluid vehicle (the “target solution / suspension”) and (b) a compressed fluid anti-solvent for the substance, and allowing the anti-solvent to extract the vehicle from the target solution / suspension so as to form particles of the target substance, wherein the target solution / suspension enters the vessel downstream of the point of entry of the anti-solvent and at a point which lies on or close to the main axis of anti-solvent flow, and wherein the anti-solvent has a sub-sonic velocity as it enters the particle formation vessel.

Description

FIELD OF THE INVENTION [0001] This invention relates to methods for use in forming particles of a target substance, and to their particulate products. BACKGROUND OF THE INVENTION [0002] It is known to use a compressed fluid, typically a supercritical or near-critical fluid, as an anti-solvent to precipitate particles of a substance of interest (a “target substance”) from solution or suspension. The basic technique is known as “GAS” (Gas Anti-Solvent) precipitation [Gallagher et al, “Supercritical Fluid Science and Technology”, ACS Symp. Ser., 406, p334 (1989)]. Versions of it have been disclosed for instance in EP-0 322 687 and WO-90 / 03782. [0003] In one particular version known as the Nektar™ SCF particle formation process (previously known as SEDS™ or “Solution Enhanced Dispersion by Supercritical fluids”), a target substance is dissolved or suspended in an appropriate fluid vehicle, and the resulting “target solution / suspension” then co-introduced into a particle formation vessel...

AI Technical Summary

Benefits of technology

[0024] The desired anti-solvent velocity is ideally achieved simply by the use of appropriate anti-solvent flow rates, back pressures and / or operating temperatures, and without the aid of mechanical, electrical and / or magnetic input such as for example from impellers, impinging surfaces especially within the anti-solvent inlet, electrical transducers and the like. Introducing the anti-solvent via a convergent nozzle, ideally as a single fluid stream, may also help in the achievement of appropriate fluid velocities. Further “energising” fluid streams, such as those required in the method of WO-97 / 31691, are not then needed in order to achieve the desired level of control over the contact between the target solution / suspension and the anti-solvent fluid.

[0084] It is believed, although we do not wish to be bound by this theory, that there may be an optimum separation between the two outlets which represents a balance between avoiding undue agglomeration of the particles as they form whilst also maximising the efficiency of fluid mixing and vehicle extraction. If the target solution / suspension is introduced into the anti-solvent flow close to the outlet of the second fluid inlet, then fluid mixing will be highly efficient and particle formation rapid, but there may also be an increased tendency for agglomeration of the particles as they form, resulting ultimately in a larger diameter product. Conversely, if the two fluids meet at too great a distance from the outlet of the second fluid inlet, then fluid mixing and vehicle extraction may be less efficient, reducing control over the product characteristics (including particle size and morphology), potentially allowing more particle growth and higher residual solvent levels and possibly also reducing yields.

Problems solved by technology

However, the authors do not appear ever to have achieved such high velocities in their experimental examples.

Images